This invention relates generally to internal combustion engines and more particularly concerns a method for generating engine calibration parameters in real-time using a mathematical model of the engine system and combustion process.
Internal combustion engines are designed and developed in several phases. At a minimum, the engine concept is assessed, the design is engineered, and the manufacturing issues are resolved. In the final phase of engine development, the engine is mapped and calibrated for optimized performance.
Engine mapping and calibration seeks to optimize the setpoints for fuel flow, airflow (including the amount of exhaust gas recirculation (EGR)), and spark ignition timing to balance the competing interests of achieving the lowest possible emissions, the best possible fuel economy, and satisfactory performance. The engine mapping and calibration process is both costly and time consuming. All potential combinations of a variety of engine operating parameters must be analyzed and associated to set points for airflow, fueling rate and spark timing. The result of the engine mapping and calibration process is a series of detailed lookup tables storing engine subsystem setpoints for these combinations of engine operating parameters. The resulting tables are stored in the powertrain control module (PCM) for use in engine control. For example, a desired EGR valve setpoint would be retrieved from the lookup table of values based upon the operating inputs of engine speed, load, and airflow, for instance.
One drawback to using calibrated look-up tables for engine control, however, is that the calibration tables are developed based upon assumptions for the engine operating environment such as the air quality and fuel grade. Thus, if the engine operating environment differs significantly from the assumed environment for which the calibration tables were developed, the engine control strategy will not be optimized. In such a case, the engine must be remapped and new calibration tables developed if the engine is to be optimized for its environment. In other words, a vehicle operating in a thin air environment such as a high altitude location may require different lookup table values than a vehicle in a very dry air environment such as a desert location. Indeed, most calibrated lookup table setpoints are actually compromised, rather than global optimized, to allow acceptable engine performance over a wider variety of operating environments.